Recuperative type heat exchanger



Oct. 29, 1968 R. s. BRAUNE ETAL 0 RECUPERATIVE TYRE HEAT EXCHANGER med Nov. 7; 1966 INVENTORS.

RUDOLF ERNST BRAUNE KARL SANDERSOVN ATTORN EYS United States Patent Oflice 3,407,870 Patented Oct. 29, 1968 3,407,870 RECUPERATIVE TYPE HEAT EXCHANGER Rudolf Ernst Braune, 22 Meadowclitf Drive, Scarborough, Ontario, Canada, and Karl Sanderson, 178 Patton St., King City, Ontario, Canada Filed Nov. 7, 1966, Ser. No. 592,513 4 Claims. (Cl. 165-83) ABSTRACT OF THE DISCLOSURE A respective heat exchanger in which an internal tube is suspended within, and in spaced relationship to, an external jacket by spacing means securing the upper end of the jacket to the tube, the lower end portion of the tube is constituted by an upwardly open channel surrounding the remainder of the tube and by a flange extending radially outwardly from the channel. The jacket at its lower end is bifurcated, having an inner portion, which is disposed in non-fluid sealing engagement within the channel, and an outer portion to the lower end of which is mounted a support base for supporting the jacket on a supporting surface surrounding, for example, a chimney stack. Inlet and outlet ports are provided in the jacket, and a flexible bellows seal is secured in a fluid-tight manner to the support base and to the flange of the internal tube.

Background of the invention This invention is concerned with a heat exchanger which is an apparatus by which heat may be transferred from one fluid to another fluid, the other fluid, prior to the heat transferance, being at a lower temperature than the first mentioned fluid A heat exchanger is frequently used to transfer heat from the hot gases of combustion, which pass to waste up the chimney stack of a smelting furnace, to the flow manner heat in the waste flue gases is transferred .to the air flowing to the furnace to maintain the combustion therein. This air is thus preheated by heat which would otherwise pass to Waste, the use of preheated air resulting in the operating efficiency of the furnace being increased.

Since the temperature of the waste flue gases as they enter the recuperator may be of the order of 1800 F.

and since the flow of air to the furnace is at the temperature of the-ambient atmospheric air there is clearly a considerable temperature differential between the elements of the recuperator which are in contact with the waste flue gases and the elements of the recuperator which are in contact with the flow of air to the furnace. This temperature differential results in a differential thermal expansion, and contraction, between the elements of the recuperator which has, in the past, resulted in considerable complication in the design and construction of recupera-, tors which would function satisfactorily throughout the range of operating temperatures encountered, it being emphasized that the flow of flue gases must under no conditions of operation of the recuperator be allowed to mix with the flow of air to the furnace, since the presence of flue gases in the flow of air to the furnace would seriously decrease the operating efiiciency of the furnace. The magnitude of the problem will be appreciated from the fact that in many recuperators, which are frequently of the order of 100 feet in height, there may be an increase of as much as 8 inches in the height of the recuperator between the inoperative or cold condition and the operative or hot condition.

It has hitherto been proposed to overcome this problem by, where the recuperator is operatively mounted in communication with the open, upper end of the chimney stack, mounting the lower end of the member which defines the passage through which the hot flue gases flow in supported contact with the said end of the chimney stack or with a fixed support structure surrounding said end of the chimney stack, the member which defines the passage through which the flow of air to the furnace passes being supported on the first-mentioned member, and means being provided at the upper and/ or lower ends of the members to accommodate the differential expansion and contraction between the members, when the recuperator is in use, and to maintain a fluid tight seal between the passages defined by the two members.

Since in this hitherto proposed construction, the memher which defines the passage through which the flue gases are caused to flow is a structural member which must not only support its own weight but also must support the weight of the other member said structural member must be of considerable strength and is therefore of relatively expensive construction either with regard to the quantity of material required or with regard to the complexity of manufacture.

Furthermore, since the thermal expansions and contractions of the structural member are transmitted to the other member and since the hot flue gases are in contact with the structural member the range of movement of the air inlet and outlet ports which are formed in said other member is considerable with the result that complicated and expensive provisions must be made to ensurethat the connecting piping to the air inlet and outlet ports remain firmly connected to these ports without excessive stressing being set up in the piping.

It is a primary object of the present invention to provide a heat exchanger which may be used as a recuperator but in which the above-mentioned disdvantages of the hitherto proposed construction of recuperator are obviated in a simple and novel manner, which is both inexpensive to manufacture and to install, and which has a high degree of efficiency in-operation.

Summary 09 the invention According to the present invention it is not the member which defines the inner passage and is constituted by an inner duct, but the member which defines the surrounding annular passage and is constituted by an outer jacket, which is supported at its lower end on a suitable supporting structure. The upper end portion of the inner duct is securely attached to the outer jacket but the duct is not a structural member and need only have suflicient strength to support itself in tension from its position of attachment to the outer jacket, from which it is suspended. The lower end portion of the inner duct is constituted by an upwardly open channel surrounding the remainder of the inner duct, and by a flange extending radially outwardly from said channel, the lower end of the outer jacket be ing bifurcated, having an inner and an outer portion. Said inner portion is disposed in non-fluid sealing engagement within said channel and said outer portion has, on the lower end thereof, a support base which serves for the above-mentioned supporting of the lower end of the outer jacket on a suitable supporting structure.

Means; such as a bellows type seal, is provided between the support base and the flange of the inner duct, the air inlet and outlet ports being formed one in the outer jacket adjacent to the upper end thereof and the other in the outer portion of the lower end of the outer jacket in communication with the channel. The seal accommodates the movement, between its positions of attachmengcaused by the differential thermal expansion and contraction between the inner duct and the outer jacket while maintaining a fluid tight seal under all operating conditions between the passage defined by the inner duct and the passage defined by the outer jacket. No significant thrust is exerted by the seal on the lower free end portion of the inner duct.

Brie) description of the drawing In order that the invention may be more clearly understood and more readily carried into effect the same will now, by way of example, be described more fully with reference to the accompanying drawing which is a half-sectioned elevation of a heat exchanger, according to a preferred embodiment of the invention, mounted as a recuperator on the open, upper end of the chimney stack of a furnace.

Description of the preferred embodiment Referring to the drawing, denotes generally an openended cylindrical tube, the upper end of which presents an outwardly directed flange having an annular portion 11 and a cylindrical portion 12 concentric with but spaced from the tube 10. Surrounding the lower end portion of the tube 10 is a further tube 13, the tube 13 being concentric with the tube 10 and the lower ends of the tubes 10 and 13 being interconnected by an annular plate 14 which thus constitutes the base of a channel 15, the walls of which are constituted by the tubes 10 and 13. The upper end of the tube 13 presents an outwardly directed flange having an annular portion 16 and a cylindrical portion 17 which is concentric with and surrounds the tube 13.

As shown on the drawing the tubes 10, 13, the annular plate 14, and the annular and cylindrical portions 16, 17, respectively, of the flange are integrally formed but, as will be clearly understood, these elements may alternatively be constituted by distinct parts which are interconnected in the manner described above by, for example, welding. Surrounding and spaced from the tube 10 is an outer jacket denoted generally by the reference 18. The jacket 18 includes a tube 19 which surrounds and is spaced from the tube 10, tubes 20 and 21 which likewise surround and are spaced from the tube 10, and an annular plate 22 which interconnects the upper ends of the tubes 20 and 21. The lower end portion of the tube 20 is disposed within the channel 15 but is spaced from the tube 13 and from the annular plate 14 as illustrated in the drawing.

The lower end of the tube 19 is secured, as by welding 23, to the annular plate 22 and the upper end of the tube 19 presents an integrally formed, inwardly directed flange 24 which is secured to the underface of an annular plate 25. Disposed parallel to and spaced above the plate 25 is a further annular plate 26, which is secured to the tube 10, by, for example, welding 27 and to the plate 25 by, in the preferred embodiment, equiangularly spaced radial strengthening vanes 28, the vanes 28 being secured as by welding to the plate 26 and to the plate 25. The vanes 28 and the plate 25 may also be secured, such as by welding, to the tube 10.

Formed in the tube 19 adjacent the upper end thereof is an air inlet port 29 comprising a length of tubing 30 the end of which remote from the tube 19 presents an outwardly directed flange 31 to facilitate connection of the port 29 to air inlet piping (not shown).

Similarly, an air outlet port 32 is formed in the tube 21 and includes a length of tubing 33 the end of which remote from the tube 21 presents an outwardly directed flange 34 to facilitate connection of the port 32 to air outlet piping (not shown).

The air outlet port 32 is disposed at a lower level than, and diametrically opposite, the air inlet port 29 as is shown in the drawing. Furthermore, the base of the port 32, when the heat exchanger is inoperative and is therefore in the cold condition is disposed substantially level with the annular portion 16 of the appropriate flange.

The heat exchanger is shown in the drawing mounted for its preferred use as a recuperator, 35 indicating the open, upper end portion of a chimney stack from a smelting furnace (not shown) and 36 indicating a portion of masonry or other construction which supports the chimney stack and from which the end portion 35 of the stack projects.

An annular base plate 37 is mounted on the masonry or other construction 36 and surrounds the end portion 35 of the chimney stack, the plate 37 being fixedly secured to the masonry 36. The lower end of the tube 21 is secured to the upper face of the base plate 37 by, for example, welding 38, a further annular plate 39 which is disposed parallel to but spaced above the plate 37 surrounding the tube 21 and being welded thereto. Interconnecting the plates 37 and 39 is a plurality of equiangularly spaced radial strengthening vanes 40 which ar secured, as by welding, to the plates 37, 39 and also, if required, to the tube 21.

A cylindrical bellows seal 41 which is preferably formed of light gauge steel is mounted with the lower end thereof secured in fluid tight engagement with the base plate 37 and with the upper end thereof secured in fluid tight engagement with the under face of the annular portion 16.

The lower end portion of the tube 10 is concentric with and surrounds the upper end portion 35 of the chimney stack, the tube 10 being a clearance fit about the portion 35 of the chimney stack so as to be freely slidable relative thereto.

When th invention is in use hot flue gases from the furnace pass upwards through the chimney stack and through the tube 10 before exhausting to the atmosphere from the upper end of the tube 10. The tube 10 constitutes in effect, a continuation in the upward direction of the chimney stack from the upper end portion 35 thereof.

Air at the temperature of the ambient atmospheric air enters the outer jacket 18 through the air inlet port 29 and flows through the recuperator in the manner hereinafter described to the air outlet port 32 and thence to the furnace for use as combustion air. In flowing through the recuperator from the air inlet port 29 to the air output port 32 the air passes in a downward direction between the inner tube 10 and the tube 19 and thence, still in a downward direction, between the inner tube 10 and the tube 20. Thereafter the air flow is reflexly directed and flows in a upward direction between the tube 13 and the tube 20 to the annular chamber bounded by the tubes 20, 21 and the annular portion 16 and plate 22 from where the air leaves the recuperator through the air outlet port 32.

The cylindrical portion 17 is a close clearance fit within the tube 21 so that there is little likelihood of air passing therebetween. Any air which does, however, pass between the portion 17 and the tube 21 is confined within the chamber bounded by the tube 21, the bellows seal 41, the portion 16, and the plate 37.

The flow of hot flue gases through the tube 10 causes thermal expansion of this tube. The upper end portion of the tube 10 is, however, substantially fixed since it is secured to the outer jacket 18 which is itself fixed to the masonry 36 at the base plate 37, so that substantially all the thermal expansion of the tube 10 occurs at the lower end of this tube, the tube 10 during this expansion being partially telescoped about the projecting upper end portion 35 of the chimney stack.

During this thermal expansion of the inner tube 10 the bellows seal 41 is compressed. The characteristics of the seal 41 are preferably such that irrespective of the operating conditions of the recuperator, any force exerted on the annular portion 16, and hence on the tube 10, by the bellows seal 41 is of negligible magnitude. A

While, when the recuperator is in the operative or hot condition, the heat content of the air which contacts the outer jacket 18 will cause thermal expansion of the jacket 18 it will be appreciated that, since the temperature of this air is considerably lower than the temjerature of the hot flue gases flowing through the tube 10, th magnitude of thermal expansions, and contractions, of the outer jacket 18 is extremely small in relation to the corresponding thermal expansions and contractions which occur in the inner tube 10. Vertical move ments of the air inlet and outlet ports 29, 31 which occur are therefore of only small magnitude and piping connections to these ports can thus readily be efiected without requiring the use of any complicated or expensive arrangements.

Contamination of the air in the outer jacket 18 by leakage of hot flue gases between the end portion 35 chimney stack and the inner tube is prevented by the presence of the bellows seal 41.

The recuperator is shown in the drawing in full lines in its inoperative or cold condition, the positions of the plate 14, the portion 16, and the tubes 10, 13 and 17 when the recuperator is in its operative or hot condition in which hot flue gases flow through the inner tube 10 being shown in broken lines. It will be appreciated that members other than those shown in dotted lines will move under thermal expansion but for purposes of clarity the positions occupied by these other members under conditions of thermal expansion have not been shown on the accompanying drawing.

What we claim as our invention is:

1. A heat exchanger comprising an inner, open-ended duct having an upper end portion and a lower end portion;

a jacket surrounding and spaced from the inner duct and defining a chamber therewith;

the jacket having an upper end and a lower end, the upper end of the jacket being joined to the inner duct for supporting the inner duct in suspension within the jacket and for closure of one end of the chamher;

the lower end portion of the inner duct being constituted by an upwardly open channel surrounding the remainder of the inner duct, and by a flange extending radially outwardly from said channel;

and the lower erid of the jacket being bifurcated, having an inner and an outer portion, said inner portion being disposed in non-fluid sealing engagement within the channel;

a support base provided on the outer portion of the lower end of the jacket for the support of the jacket on a supporting structure;

means interconnecting the support base and the flange of the inner duct for closing the end of said chamber remote from said one end thereof while permitting free movement of the lower end portion of the inner duct relative to the jacket;

and spaced inlet and outlet ports one of which is formed in the jacket in communication with said chamber and the other of which is formed in the outer portion of the lower end of the jacket in communication with the channel.

2. A heat exchanger as claimed in claim 1 wherein said means interconnecting the support base and the flange of the inner duct comprises a flexible sealing member.

3. A recuperator comprising:

an external jacket having an upper end and a lower end;

an internal tube having an upper end portion and a lower end portion;

spacing means securing the upper end of the external jacket to the upper end portion of the internal tube in fluid-tight manner;

the internal tube being freely suspended from the spacing means;

the lower end portion of the internal tub being constituted by an upwardly open channel surrounding the remainder of the internal tube, and by a flange extending radially outwardly from said channel;

and the lower end of the external jacket being bifurcated, having an inner and an outer portion, said inner portion being disposed in non-fluid sealing engagement within said channel;

a support base secured to the lower end of said outer portion and mounted on a support surface surrounding an upwardly open end of a chimney stack for heated exhaust gases from a furnace;

flexible sealing means secured in fluid-tight manner to the support base and to the flange of the internal tube for permitting relative movement between the lower end portion of the internal tube and the external jacket under conditions of differential expansion or contraction thereof; the lower end portion of the internal tube surrounding in telescopic relationship, the upwardly opening end of the chimney stack;

and vertically spaced air inlet and outlet ports one of which is formed in the external jacket adjacent to the upper end thereof and the other of which is formed in the outer portion of the lower end of the external jacket in communication with the channel.

4. A recuperator as claimed in claim 3 wherein the flexible sealing means comprises a vertically disposed flexible bellows seal.

References Cited UNITED STATES PATENTS 2,468,903 5/ 1949 Villiger -155 2,942,855 6/1960 Wellensiek 165-154 3,185,210 5/1965 Kuhne et a1 165-83 XR 3,187,808 6/1965 Kuhne et al 16583 3,189,086 6/1965 Esser et al. 16583 XR FOREIGN PATENTS 624,749 8/ 1961 Canada.

ROBERT A. OLEARY, Primary Examiner M. A. ANTONAKAS, Assistant Examiner. 

